This invention relates to a method of manufacturing a seat cushion which is satisfactorily permeable to air and provides a comfortable feeling to sit thereupon when used for seats in automobiles and various types of furniture.
A covering material such as a fabric material with or without a vinyl coating is most commonly used in many of prior art seat cushions for seats in automobiles. One of typical prior art processes employed for the manufacture of a seat cushion of this kind comprised the steps of cutting a web of fabric material with or without a vinyl coating into pieces corresponding to the portions including the seating portion and side portions, sewing together these pieces of fabric material to form a seat surface covering of bag-like structure, inserting a filler pad of cushion providing material such as foamed polyurethane into the internal space of the seat surface covering of bag-like structure, and mounting the resultant assembly on a seat frame provided with springs.
However, such a prior art manufacturing process required an extended time and a lot of labor. In addition, the prior art process was defective in that twists and creases impairing the beautiful appearance of the products occurred frequently, and some of the products were extremely distorted to such an extent that the remedy thereof required also an additional extended time and much labor, together with an additional cost.
In an effort to obviate these prior art defects, there has been recently proposed a method of manufacturing a seat cushion by applyilng a back coating of vinyl or like material to a seat-covering providing fabric material for the purpose of shaping under vacuum, heating the fabric material, shaping the fabric material into the form of a seat surface covering of bag-like structure by use of shaping dies or any other suitable means, and in lieu of inserting a filler pad of cushion providing material into the seat surface covering of bag-like structure, injecting a solution of polyurethane into the internal space of the seat surface covering of bag-like structure to integrally mold foamed polyurethane with the seat surface covering being retained between the dies. Such an integral molding process obviates the aforementioned prior art defects, and a distinct embossed pattern can be produced on the product.
However, such a method finds a limited application and is only applicable to vinyl-coated fabric materials or fabric materials having a back coating of vinyl or like material. Further, in the product obtained by the integral molding of foamed polyurethane with the seat surface covering of fabric material, the poplyurethane solution tends to penetrate through the texture thereby hardening the seat surface covering or producing blurs on the surface thereof, or the solution may solidify to impair the otherwise beautiful appearance of the product. Thus, the seat cushion obtained by the proposed method has been defective in that the seat surface covering has no permeability to air, the otherwise beautiful external appearance is impaired, and the seat cushion does not provide the desired comfortableness to sit thereupon.
A prior art seat cushion obtained by bonding a filler pad of foamed polyurethane to a seat surface covering of fabric material of bag-like structure has also been defective in that a thin layer tending to be formed on the surface of the filler pad of foamed polyurethane by, for example, the mold releasing agent used in the molding step deteriorates the permeability to air and acts as a source of unusual noise, and also, separation of the bonded portions together with stripping of the thin surface layer tends to occur.
Further, an integrally molded product having a defect in its seat surface covering of fabric material or a defect in the foamed polyurethane, which is the cushion providing material, must be wasted as a reject resulting in a low yield rate of final products.
Further, the material costs have become necessarily high when a single seat surface covering of highly extensible fabric material is used to continuously cover the seat cushion portions including the seating portion and side portions to meet a specification requirement. Further, when the seat cushion includes undercuts in its side portions, it has been very difficult to cover the side portions besides the seating portion with the single seat surface covering.